This application is based on and incorporates herein by reference Japanese Patent Application Nos. 2000-317810 filed on Oct. 18, 2000, and 2001-56075 filed on Mar. 1, 2001.
1. Field of the Invention
The present invention relates to a control apparatus for an internal combustion.
2. Description of Related Art
There has been conventionally known a valve timing control apparatus for advancing and retarding intake and exhaust valve timing by changing the phase of camshaft rotation in accordance with an engine speed. In the internal combustion engine in which the fuel is injected into an intake pipe, not limited to the internal combustion engine equipped with a fuel injection valve, the fuel injected from the fuel injection valve sticks to the intake pipe. When the engine is running in a steady state, the amount of vaporized portion of the fuel sticking to the intake pipe and the amount of a part of the fuel injected from the fuel injection valve and newly sticking to the intake pipe are balanced. The air-fuel ratio, therefore, will not be affected by the amount of the fuel sticking to the intake pipe.
However, when the driver turns off the ignition switch in an attempt to stop the engine, the fuel sticking to the intake pipe will remain in the intake pipe. In this state, when the ignition switch is turned on to restart the engine, the fuel to be injected from the fuel injection valve and also the fuel remaining in the intake pipe are both drawn for combustion into the combustion chamber, thereby not only enriching the air-fuel ratio but producing much of HC emissions. Particularly upon starting the engine cold, the catalyst is not activated and therefore HC emissions will be discharged out to the atmosphere without being cleaned.
Further, the variable valve control apparatus in practical use is in most cases designed to change the intake valve timing and lift. For example, in partial-load operation, the intake valve timing is advanced to increase the amount of valve overlap to increase the amount of internal EGR gases (residual gases) and to reduce a pumping loss for improving fuel economy, and also to warm up the intake air by the internal EGR to accelerate atomization of injected fuel and accordingly to reduce the amount of HC emissions.
During idling or low-load operation when a small amount of air is taken in, the intake valve timing is advanced (the amount of valve overlap is increased) to increase the amount of internal EGR gases, residual gases are blown back to the intake side, to disturb the charge of the intake air into the engine cylinder. There is, therefore, a possibility of aggravation of exhaust emissions due to poor fuel combustion, and unstable engine rotation because of increased engine vibration. In this case, however, if the intake valve timing is retarded (the amount of valve overlap is decreased) and the amount of internal EGR gases is reduced for the purpose of improving combustion stability by achieving an intake air charging performance, the intake air warm-up effect by the internal EGR gases will decrease, thereby failing in gaining the effect of decreasing the amount of HC emissions.
That is, in a system, like a conventional system, which changes the operation characteristics of the intake valve (valve timing and lift) during the intake stroke, when the operation characteristics of the intake valve are controlled toward improving the intake air warm-up performance, the system is likely to operate to lower the intake air charge performance. Under such an operating condition, both the intake air warm-up performance and the charge performance cannot exist on a high level. Therefore, it is impossible to satisfy such increasingly strict requirements for improving exhaust emissions, fuel economy, and stability of engine operation.
A first object of the present invention is to provide a control apparatus for an internal combustion engine which is capable of reducing an amount of fuel sticking to an intake pipe after the internal combustion engine is stopped.
According to a first aspect of the present invention, an intake-exhaust valve timing setting means of a control apparatus for internal combustion engine sets a valve timing of at least one of an intake valve and an exhaust valve to a specific valve timing. At this specific valve timing, it is possible to reduce the amount of fuel sticking to the intake pipe of the internal combustion engine by detecting that an ignition switch is turned off by an ignition signal detecting means.
Since the above-described control is conducted after the ignition switch is turned off, the amount of fuel sticking to the intake pipe can be reduced. Therefore, much of HC emissions will not occur when the catalyst is still in a state before activation at the time of subsequent engine starting. It is, therefore, possible to control the discharge of the HC emissions out into the atmosphere.
The variable valve timing mechanism of the present invention may be either a variable intake valve timing mechanism which controls only the intake valve timing, or may be a variable exhaust valve timing mechanism which controls only the exhaust valve timing, or may be a variable intake-exhaust valve timing mechanism comprising a combination of both valve timing mechanisms. The catalyst may be a catalyst having a capacity to adsorb, to absorb and store, and/or to clean the HC emissions. For example, the catalyst may be a three-way catalyst or an HC adsorbing catalyst. Furthermore, the valve timing mechanism of the present invention may be a valve timing mechanism which changes the valve timing by variably setting the lift, or may be such valve timing mechanism that freely sets both the lift and the valve timing.
According to a second aspect of the present invention, a method for controlling an internal combustion engine is provided with a variable valve timing mechanism which freely sets the valve timing by driving at least one of an intake valve and an exhaust valve which open and close the intake air passage and the exhaust gas passage communicating with the combustion chamber of the internal combustion engine, and the catalyst provided in the exhaust gas passage to adsorb and/or clean the exhaust gases discharged from the internal combustion engine. This control method has two steps: detecting the ignition switch turned to off, and setting the valve timing of at least one of the intake valve and exhaust valve to a specific value for reducing the fuel sticking to the intake pipe of the internal combustion engine after detecting the ignition switch in off position.
Thus, it is possible to reduce the amount of fuel sticking to the intake pipe interior. Therefore, at the time of subsequent engine starting, little amount of fuel sticking to the intake pipe interior if the catalyst for occluding, adsorbing and/or cleaning discharged HC emissions is not in an activated state, thereby enabling the reduction of the HC emissions.
A second object of the present invention is to provide a valve control apparatus for an internal combustion engine which is capable of achieving both an intake air warm-up performance and an intake air charge performing on a high level, and also is capable of improving exhaust emissions, fuel economy, and stability of engine rotation.
There has recently been developed a valve control apparatus which can easily drive intake and exhaust valves by an electromagnetic actuator without regard to the crank angle, and control the electromagnetic actuator by an engine control circuit (a valve control means).
With attention paid to this point, according to a third aspect of the present invention, a valve control means controls the intake valve to open multiple times per cycle of rotation of the internal combustion engine. By designing the valve control device, it is possible to separately open, per cycle, the intake valve to warm up the intake air with combustion gases in the cylinder and to charge the intake air into the cylinder at the optimum timing, thereby achieving both the intake air warm-up performance and charge performance on a high level. Therefore, the fuel economy and the stability of engine rotation can be enhanced by the effect of improving combustion stability by achieving the intake air charge performance while reducing the amount of HC emissions through the effect of reducing a wet portion of injected fuel by the warmed-up intake air and the effect of accelerating atomization (the effect of improvement in combustibility).